In an electrophotographic copying machine, a digital copier, a laser printer and so forth, it is popular to employ an electrophotographic photoreceptor comprising a photoreceptive layer provided to the top of a (photoreceptor) base of a rotary drum-like electrophotographic photoreceptor (hereinafter sometimes abbreviated to a "base"). As for the materials of a base constituting such an electrophotographic photoreceptor as mentioned above, an aluminium material is preferably used, because of the advantages of its low cost, light weight and processing convenience. A technique for making use of a base of an electrophotographic photoreceptor comprising an aluminium alloy containing silicon and iron each in a proportion within a specific range is disclosed in JP OPI Publication No. 64-86152/1989. A technique for making use of a base of an electrophotographic photoreceptor comprising an aluminium alloy containing silicon, magnesium and iron each in a proportion within a specific range is disclosed in JP OPI Publication No. 64-86154/1989. A technique for making use of a base of an electrophotographic photoreceptor comprising an aluminium alloy containing magnesium, silicon, copper and titanium each in a proportion within a specific range is disclosed in JP OPI Publication No. 64-86155/1989. A technique for making use of a base of an electrophotographic photoreceptor comprising an aluminium alloy containing silicon, iron and magnesium each in a proportion within a specific range and other metals each in a proportion not more than a specific range is disclosed in JP OPI Publication No. 1-123245/1989. A rotary drum type base comprising an aluminium material is generally finished up by cutting the surface of a tubular-shaped raw material. In a cutting process, a cutting fluid is commonly used. A cutting fluid is used for the purposes of cooling, lubricating and washing. The cutting fluids include, typically, those of the petroleum type, polybutene type, kerosene type, white kerosene type and the like. After cutting a base, the base surface is also washed by contact type washing means utilizing a brush and/or an abrasive, for preventing a defective image production.
As for the concrete techniques relating to a method for surface processing of a photoreceptor base of an electrophotographic photoreceptor, the following techniques have so far been proposed.
(1) A technique for processing the base of an electrophotographic photoreceptor, by making use of a cutting oil containing an oiliness improving agent and/or an extreme-pressure additive in a proportion of not more than 10% by weight, (See Japanese Patent Publication Open to Public Inspection -hereinafter referred to as JP OPI Publication- No. 63-307463/1988);
(2) A technique for finishing the surface of the base of an electrophotographic photoreceptor comprising an aluminium alloy containing magnesium, silicon, copper and titanium each in a proportion within a specific range, by making use of a cutting tool having a rounded cutting portion, (See JP OPI Publication No. 64-86151/1989);
(3) A technique for finishing the surface of the base of an electrophotographic photoreceptor comprising an aluminium alloy containing magnesium, silicon and copper each in a proportion within a specific range, by making use of a cutting tool having a rounded cutting portion, (See JP OPI Publication No. 64-86153/1989);
(4) A technique for making use of a surface-processing apparatus that is comprised of a lathe unit, a high-pressure liquid blasting unit and a unit for transporting a base of an electrophotographic photoreceptor, so that the lathe processing and the high-pressure blasting processing can be performed successively and automatically, (See JP OPI Publication No. 1-172573/1989);
(5) A technique in which the base surface of an electrophotographic photoreceptor is so roughened as to have a specific surface roughness by scanning a nozzle connected to a high-pressure water supply source along the surface of the base, with jetting high-pressure water from the orifice of the nozzle to the surface of the base of the electrophotographic photoreceptor, (See JP OPI Publication No.. 63-264764/1988).
In the above-mentioned conventional techniques, however, there may be some instances where an environmental extraneous matter such as aluminium chip, dust and dirt, rust and the like fixedly adhere to a base in such a state where they are incorporated into a cutting oil. For example, if such a state as mentioned above should be allowed to stand for such a long period as for one month or longer and, particularly, under the high temperature and high humidity conditions, the above-mentioned adhered matter is further solidly fixed to the base and the surface of the base is partly corroded (or rusted). There may also be some instances where the corrosion may not be visually confirmed.
Such a corrosion as mentioned above cannot completely be removed neither by dipping a corroded base surface in an organic solvent or a surfactant solution nor by making such a non-contact cleaning as a ultrasonic cleaning and a UV ray/O.sub.3 irradiation cleaning. Therefore, when an electrophotographic photoreceptor is constituted by providing a photoreceptive layer to the surface of a base having such a corrosion as mentioned above, an image defect is produced on the corroded portions.
A partial corrosion produced on the surface of a base may be removed to a certain extent by applying a contact cleaning to the base surface with a brush or an abrasive. However, the base surface is scratched according to an aluminium material used, and a photoreceptive layer, particularly a carrier-generation layer, formed on the scratched portion is liable to vary the layer thickness thereof. Therefore, the photoreceptive speed of the photoreceptive layer is so varied as to raise such a problem that a contrast is produced in a halftone image and an image will result in defect.
With a base comprising an aluminium material surface-processed by making use of a cutting oil as in the conventional techniques and for satisfactorily removing the cutting oil therefrom, a cleaning should be made with a fluorocarbon such as Freon 11, 112 and 113, or a chlorine type solvent such as those of trichloroethylene, 1,1,1-trichloroethane, parchloroethylene or methylene chloride. From the viewpoints of ozonosphere destruction and carcinogenicity, it is, therefore, problematic on the environmental pollution and operation safety to make use a lot of such a solvent as mentioned above.
The foregoing technique (5) is to process the surface of a base while jetting high-pressure water. However, there raises such a problem that the surface of a base can hardly be processed uniformly by only jetting high-pressure water.
The foregoing techniques are so developed as to solve the above-mentioned problems.
(6) A technique for cutting the surface of the base of an electrophotographic photoreceptor comprising an aluminium material by making use of a cutting tool comprising a polycrystal diamond sintered compact, with supplying a cutting fluid comprising water to the base surface, (See JP Application No. 2-417448/1990);
(7) A technique for cutting the surface of the base of an electrophotographic photoreceptor comprising an aluminium material by making use of a cutting tool comprising a polycrystal diamond sintered compact, with supplying a cutting fluid comprising a surfactant or an aqueous solution of water-soluble organic solvent to the base surface, (See JP Application No. 2-417449/1990);
(8) A technique for cutting the surface of the base of an electrophotographic photoreceptor comprising an aluminium material by making use of a cutting tool comprising a polycrystal diamond sintered compact, with supplying a cutting fluid comprising a water-soluble organic solvent without containing water to the base surface, (See JP Application No. 2-417447/1990);
According to these techniques, the cause of an image defect was traced as follows. A cut chip, environmental extraneous matter or the like, that is produced when a base was surface-processed, it is fixed to the base surface, through an cutting oil as a binder or it is strongly fixed thereto by decomposing the cutting oil itself and, further, it is strongly fixed thereto by a chemical reaction. The foregoing techniques (6) through (8) each to solve the foregoing problems by making use of water, an aqueous surfactant solution, an aqueous solution of a water-soluble organic solvent or a cutting fluid comprising a water-soluble organic solvent without containing water, each in place of a cutting oil, and then by applying a cutting process to a base surface with the use of a cutting tool comprising a polycrystal diamond sintered compact.
However, the surface of the above-mentioned base of photoreceptor for electrophotography obtained by means of a polycrystal diamond cutting tool does not show a satisfactory specular gloss, having a certain amount of unevenness. On the other hand, in order to produce a photoreceptor having high sensitivity, it is necessary to reduce the thickness of a subbing layer on which a light-sensitive layer is coated. Accordingly, in the case of a base of photoreceptor obtained by the use of a polycrystal diamond cutting tool, the thickness of subbing layer must be increased for flattening the unevenness mentioned above. Therefore, it was difficult to manufacture a photoreceptor having high sensitivity.
Incidentally, a technology to mirror-finish the surface of the base of photoreceptor for electrophotography by means of a monocrystal diamond cutting tool has been known. The mirror-finishing method using a monocrystal diamond cutting tool smoothens the surface of the base through burnishing action of the edge of the blade of the cutting tool which removes unevenness of the surface of the base.
However, the above-mentioned mirror-finishing method by the use of the monocrystal diamond cutting tool requires much lubrication. Accordingly, it was ordinary to use an oil cutting liquid. In addition, the mere replacement of oil cutting liquid with aqueous cutting fluid does not result in a specular gloss on the surface of the base, rather, causing scratches.
Accordingly, so far, an oil cutting fluid has been thought necessary for a mirror-finishing method using a monocrystal diamond cutting tool and use of aqueous cutting fluid has been thought impossible.